You'd get it the same way you'd figure out the total amount spent on fast food. You look at each purchase and add them together.
You'd get it the same way you'd figure out the total amount spent on purchasing games. You'd look at each purchase and add them together.
In other words, to figure out the total amount you have spent on Silver, you'll have to look at each purchase. There is no metric available that adds up all of your purchases into one number itself. So, you have to go through each item individually that you have purchased, which is the thing you don't want to do, but there's no other way.